Recourse to zeolite crystals of very small sizes, especially nanometric, is of great interest when excellent transfer properties are desired. There are at the present time mainly three synthetic methods for obtaining small-sized crystals, as taught in many publications (see for example T. Tago and T. Masuda, Zeolite Nanocrystals—Synthesis and Applications, chapter 8, “Nanocrystals”, published by INTECH, (2010), 326 pages, or Vuong-Gia Thanh, PhD dissertation “Synthesis and characterization of nanozeolites”, December 2006, University of Laval, Quebec).
These three synthetic methods may be summarized as follows:    1) synthesis in very dilutive medium and at low temperature, most of the time below room temperature; these techniques have the drawback of being long and sparingly economical in industrial terms;    2) synthesis in confined spaces such as the pores of carbon matrices, microemulsion droplets, polymer hydrogels and the like; and    3) synthesis with growth inhibitors, optionally in the presence of an organic solvent, which are introduced into the reaction mixture after the maturation phase and which are directed toward limiting the crystal growth; these processes are sparingly economical on account of the relatively long synthesis times; T Tago et al. (ibid.) propose, for example, nonionic surfactants such as polyoxyethylene-based ethers or ionic surfactants such as cetyltrimethylammonium bromide (CTAB) or sodium bis(2-ethylhexyl)sulfosuccinate (AOT), which lead to relatively long synthesis times, of the order of several days.
Patent application JP2009155187 discloses the synthesis of a colloidal zeolite of faujasite type (FAU) with an SiO2/Al2O3 ratio of between 2 and 6, having a bipopulation of particles with a first mean diameter of between 20 nm and 200 nm and a second mean diameter of between 20 nm and 800 nm, the ratio of these mean diameters ranging from 1 to 5 and the network constant (UD) being between 24.60 Angströms and 24.90 Angströms. The purpose sought in said application is to obtain very sparingly agglomerated crystals.
Patent JP2008230886 presents the synthesis of relatively uniform small particles by seeding with a transparent solution of nuclei, i.e. of very small nuclei, obtained after a very long maturation time, i.e. more than 100 hours. This process thus appears for this reason to be uneconomical and industrially unenvisageable.
The synthesis, filtration and handling of nanometric solids of this type are, however, difficult, not only on account of the small sizes of said solids, but also on account of their low density.
Attempts to make the handling of such nanometric solids less difficult are illustrated, for example, by US2012100066 which teaches a means for recovering zeolite nanocrystals by centrifugation followed by a phase of placing in contact with a solution that allows agglomeration of the crystals with each other.
Certain authors teach that such small zeolite objects may be aggregated in the form of secondary particles which are easier to handle and which will conserve satisfactory transfer properties. Thus, for example, patent application US 20120227584 proposes FAU zeolite nanocrystal aggregates with a mean diameter of greater than or equal to 0.8 μm, the mean diameter of the nanocrystals being less than or equal to 0.3 μm, and in which at least 80% of the primary particles (nanocrystals) are aggregated. In this case also, the synthesis, performed in dilute medium, is long, uneconomical and consequently industrially unenvisageable.
In addition, the zeolite objects must have substantial or even maximum crystallinity, in terms of the Dubinin-Raduskevitch volume and the purity of the crystalline phase obtained by x-ray diffraction (XRD).
There thus remains at the present time a need for an economical, readily industrializable process for synthesizing zeolite nanocrystal aggregates having substantial or even maximum crystallinity.